Apple: "We don't want Google Voice on the iPhone, period. But we'll publicly tell Google they're fine to put it on as a handicapped web app, because we couldn't stop that anyway, and it makes us look like we don't have anything against it. But we do. We are worried that Google will convert the iPhone into a shell for its own products, which is why we're talking to other search engines and are (probably) building our own Maps app."
Google: "Fine. We'll build a web app, and it will be sort of shitty. But we'll keep updating it with the latest HTML5 tricks and make it pretty damn good for a web app — far better than most other companies could do anyway. We're going to release Google Voice to the public later this year, and iPhone users will be able to try it for themselves with the web app. When they find out that the experience would be even better if Apple would approve our native app, maybe we'll see a grassroots movement. Maybe not. Either way, we're keeping our best native apps on Android."
To anyone who thinks that Apple is worried about the user experience and reproducing core functionality, that's all misdirection. There are plenty of applications that similarly reproduce some of the iPhone's core functionality. There are a few apps that do EXACTLY what Google Voice does, but are targeted at a different market. Apple is trying to keep its control over the iPhone for competitive reasons, not because they're worried about user confusion.